code: def check_for_acyclicity(graph):
      msg = (
          "There is a loop in your flow: *{0}*. Break the loop "
          "by fixing self.next() transitions."
      )
  
      def check_path(node, seen):
          for n in node.out_funcs:
              if n in seen:
                  path = "->".join(seen + [n])
                  raise LintWarn(
                      msg.format(path), node.tail_next_lineno
                  )
              else:
                  check_path(graph[n], seen + [n])
  
      for start in graph:
          check_path(start, [])
  
imports: import re
  from .exception import MetaflowException
  from .util import all_equal
label_desc: Use image node_id 9 for calling a global function with example usage: check_for_acyclicity(graph) without return types